Processing apparatus, mobile communication system, base station apparatus, method for switching connection of mobile station, and non-transitory computer readable medium storing program

ABSTRACT

A processing apparatus operates aiming to realize handover to each mobile station while reducing a failure rate of the handover even when PSC Confusion is generated. More specifically, when a connection of the mobile station is switched from a first base station to a second base station, the processing, apparatus determines the second base station by selecting from a plurality of base stations according to connection history information indicating a success or a failure of past switching of the connection from the first base station to at least one of the plurality of base stations.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

Japan Priority Application 2009-286823. filed Dec. 17, 2009 includingthe specification, drawings, claims and abstract, is incorporated hereinby reference in its entirety. This application is a Continuation of U.S.application Ser. No. 13/515,462 (National Stage of PCT/JP2010/007304),filed Dec. 16, 2010 incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a handover method in a mobilecommunication system, and particularly to a handover method in a mobilecommunication system regarding HNB (Home Node B).

2. Background Art

Currently, the development of small base stations that can be installedin a user's house, office, and the like have been advanced. 3GPP (ThirdGeneration Partnership Project) defines such a small base station asHome Node B (HNB), and proceeds with standardization.

In 3GPP, a spreading code called PSC (Primary Scrambling Code) isdefined. The PSC is defined in a range of 512 from 0 to 511. In the HNB,one cell (area where the HNB can communicate) can use only one PSC.Further, one cell must use one PSC.

A handover procedure between the HNBs agreed in 3GPP Release 9 isexplained below (NPL 1). The following explanation assumes Intra HNB-GWand Intra CSG. The Intra HNB-GW indicates the state where the HNB towhich a mobile station (UE) is connected (hereinafter referred to as aSource HNB) and the HNB to be a handover destination (hereinafterreferred to as a Target HNB) are connected to the same HNB-GW (Home NodeB Gateway). Further, the Intra CSG (Closed Subscriber Group) indicatesthat the Source HNB and the Target HNB are broadcasting the same CSG-ID.Note that the CSG is a method for realizing access control to the HNBdefined in the 3GPP Release 8. The HNB to which this method is appliedis assigned with a certain CSG-ID and broadcasts it inside its own cell.The UE accesses the HNB only when the communication to the CSG-ID isallowed.

FIG. 20 is a sequence diagram showing the handover procedure between theHNBs agreed in the 3GPP Release 9. First, the UE is in the state ofcommunication with CS (Circuit Switch) or RS (Packet Switch) (S101).

When the UE satisfies the condition to execute handover from the HNB incommunication (Source HNB) to another HNB (Target HNB), PSC used by theTarget HNB is notified to the Source HNB by an RRC (Radio ResourceControl):MEASUREMENT REPORT message (S102). The UE identifies the HNB bythe PSC.

When the Source HNB receives the RRC:MEASUREMENT REPORT message from theUE, the Source HNB identifies the Target HNB by the PSC included in themessage. Each HNB holds information (PSC, Cell ID, RNC-ID, frequencyinformation, and the like) of neighbor HNBs. Note that the RNC-ID (RadioNetwork Controller Identifier) indicates an ID assigned to catch HNB.Each HNB identifies the RNC-ID of the HNB which uses the received PSCaccording to the information held by each HNB (S103).

The Source HNB transmits an RUA (RANAP User Adaption):DIRECT TRANSFERmessage including the RNC-ID of the Target HNB to the HNB-GW (S104). ARANAP:(Radio Access Network Application Part) RELOCATION REQUIREDmessage is encapsulated in the RUA:DIRECT TRANSFER message.

Note that the RANAP is signaling exchanged between RNC and CN (CoreNetwork) in a macro network of a related art. In a network using theHNB, it is a protocol used between the HNB and the CN. Further, the RUAis a protocol used on an luh interface.

The HNB-GW which received the RANAP:RELOCATION REQUIRED messageidentifies the Target HNB with the corresponding RNC-ID (S105). TheHNB-GW transmits the RANAP:RELOCATION REQUEST message encapsulated inthe RUA message to the Target HNB (S106). Note that the name of the RUAmessage is still not determined at the present stage. In the followingexplanation, the message with an undetermined name is referred to as“XXX” (for example, RUA:XXX) in each protocol specification.

When the Target HNB receives RANAP:RELOCATION REQUEST message, theTarget HNB registers information on the UE that performs handover andsecures a resource for the UE (S107). Then, the Target HNB transmits theRUA:DIRECT TRANSFER message encapsulating a RANAP:RELOCATION REQUESTACKNOWLEDGE message to the HNB-GW (S108).

The HNB-GW which received the RUA:DIRECT TRANSFER message transmits aRANAP:RELOCATION COMMAND message to the Source HNB (S109). After that, awireless synchronous process (S111) is performed between the UE and theTarget HNB. Next, the Target HNB notifies that the relocation iscompleted to the HNB-GW (S114). Then, the Source HNB completes a seriesof handover processes by the HNB releasing, the resource of the UE(S116).

CITATION LIST

Non Patent Literature

NPL 1: 3GPP TS 25.467 “UTRAN architecture for 3G Home Node B (HNB);Stage 2”, 3GPP, Searched on Nov. 24, 2009, the Internet<URL:http://www.3gpp.org/ftp/Specs/archive/25_series/25.467/25467-901.zip>

SUMMARY OF THE INVENTION

1. Technical Problem

However, there is a problem generated that in the abovementioned HNBprocedure, the handover is not normally executed when PSC Confusion isgenerated. Details of the problem are explained below.

The problem is generated when the same PSC as the PSC for a cell of theHNB, which is a desired handover destination, is used by another cellwhen the UE performs handover. This state is referred to as the PSCConfusion. When the PSC Confusion is generated, it becomes difficult forthe Source HNB to accurately determine the Target HNB in S103 of FIG.20, That is, when a plurality of HNBs have the same PSC, it becomesdifficult to identify the RNC-ID of the Target HNB.

A system for the Source HNB to select one HNB (select the RNC-ID) as theTarget HNB at random is examined here. Even in this system, when theSource HNB selects a different HNB from the HNB desired by the UE to bethe handover destination, the handover fails.

Accordingly, in order to prevent from generating failures in thehandover, even when the PSC Confusion is generated, it is required toincrease the success rate of the handover.

The present invention is made in order to solve a problem, and aims toprovide a mobile communication system that can reduce the failure rateof the handover even when the PSC Confusion is generated.

SOLUTION TO PROBLEM

An exemplary aspect of the present invention is a mobile communicationsystem that includes a first base station that generates a first celland can be connected to a mobile station, a gateway apparatus thatcommunicatively connects the first base station and a plurality of basestations to a higher-level network and a processing means that, when aconnection of the mobile station is switched from the first base stationto a second base station that is included in the plurality of basestations, selects the second base station from the plurality of basestations according to connection history information indicating asuccess or a failure of past switching of the connection from the firstbase station to at least one of the plurality of base stations.

Another exemplary aspect of the present invention is a processingapparatus that, when a connection of a mobile station is switched from afirst base station to a second base station, selects the second basestation from a plurality of base stations according to connectionhistory information indicating a success or a failure of past switchingof the connection from the first base station to at least one of theplurality of base stations.

Another exemplary aspect of the present invention is a method forswitching a connection of a mobile station that includes evaluating by amobile station whether or not a condition for switching the connectionfrom a first base station to a second station is satisfied, and when thecondition for switching the connection is satisfied, selecting thesecond base station from a plurality of base stations according toconnection history information indicating a success or a failure of pastswitching of the connection from the first base station to at least oneof the plurality of base stations.

Another exemplary aspect of the present invention is a base stationapparatus that, when receiving a connection switch request from a mobilestation in connection to a desired base station apparatus, transmits toa processing apparatus information of whether or not a same spreadingcode is assigned to the desired base station apparatus and another basestation apparatus.

Another exemplary aspect of the invention is a base station apparatusthat transmits spreading code and frequency information that is used bythe base station apparatus to a processing apparatus for selecting thebase station apparatus to which a mobile station is connected.

Another exemplary aspect of the present invention is a gateway apparatusfor communicatively connecting a plurality of base stations to ahigher-level network that stores spreading code information andfrequency information used by at least one or more base stations, andwhen a connection of a mobile station is switched from a first basestation to a second base station, selects the second base station fromthe plurality of base stations according to connection historyinformation indicating a success or a failure of past switching of theconnection from the first base station to at least one of the pluralityof base stations.

A non-transitory computer readable medium storing a program according tothe present invention that causes a computer to execute a process ofcontrolling connection switch of a mobile station from a first basestation to a second base station, in which the non-transitory computerreadable medium stores a program that, when the connection of the mobilestation is switched from the first base station to the second basestation, selects the second base station from a plurality of basestations according to connection history information indicating asuccess or a failure of past switching of the connection from the firstbase station to at least one of the plurality of base stations.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a mobilecommunication system that can reduce the failure rate of the handovereven when the PSC Confusion is generated.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram showing a basic configuration of a mobilecommunication system according to a first exemplary embodiment;

FIG. 2 is a block diagram showing the basic configuration of the mobilecommunication system according to the first exemplary embodiment;

FIG. 3 is a view showing a list of neighbor cells held by HNB#a100according to the first exemplary embodiment;

FIG. 4 is a view showing a process overview of HNB RegistrationProcedure of HNBAP according to the first exemplary embodiment;

FIG. 5 is a view showing a table in a database inside HNB-GW100according to the first exemplary embodiment;

FIG. 6 is a view showing an HNB REGISTER REQUEST message according tothe first exemplary embodiment;

FIG. 7 is a view showing an RUA:DIRECT TRANSFER message according to thefirst exemplary embodiment;

FIG. 8 is a sequence diagram showing an operation of the mobilecommunication system at the time of executing handover according to thefirst exemplary embodiment;

FIG. 9 is a view showing a table in a database storing history ofhandover results according to the first exemplary embodiment;

FIG. 10 is a sequence diagram showing an operation of the mobilecommunication system at the time of executing handover according to thefirst exemplary embodiment;

FIG. 11 is a view showing a list of handover destination candidatesaccording to the first exemplary embodiment;

FIG. 12 is a flowchart showing a process when a Source HNB determines aTarget HNB according to the first exemplary embodiment;

FIG. 13 is a flowchart showing a process when HNB-GW110 determines theTarget HNB according to the first exemplary embodiment;

FIG. 14A is a view of Target ID included in a RANAP:RELOCATION REQUIREDmessage according to a second exemplary embodiment;

FIG. 14B is a view of the Target ID included in the RANAP:RELOCATIONREQUIRED message according to the second exemplary embodiment;

FIG. 15 is a view showing a configuration of HNB according to a thirdexemplary embodiment;

FIG. 16 is a sequence diagram showing an operation of a mobilecommunication system at the time of executing handover according to thethird exemplary embodiment;

FIG. 17 is a view showing a table in a database storing history ofhandover results according to the third exemplary embodiment;

FIG. 18 is a sequence diagram showing an operation of the mobilecommunication system at the time of executing handover according to thethird exemplary embodiment;

FIG. 19 is a flowchart showing a process when a Source HNB determines aTarget HNB according to the third exemplary embodiment; and

FIG. 20 is a view showing an operation of a mobile communication systemat the time of executing handover according to a related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, specific exemplary embodiments incorporating the presentinvention are explained in detail with reference to the drawings. Samecomponents are denoted by the reference numerals in each drawing, andrepeated explanation is omitted as necessary for the clarity of theexplanation.

First Exemplary Embodiment

Hereinafter, an exemplary embodiment of the present invention isdescribed with reference to the drawings. First, with reference to FIG.1, a basic configuration of a mobile communication system and anoverview of the operation thereof according to the first exemplaryembodiment are explained.

A base station a 10 holds information (PSC and the life) of a cellcomposed of the base station a10 and base stations (a base station b20,a base station c30, and a base station d40) that compose neighbor cells.A gateway apparatus 50 is disposed between the base stations a10, b20,c30 and d40 and higher-level network (such as a core network of acarrier), and connects these base stations communicatively to thehigher-level network. The gateway apparatus 50 relays user data andcontrol data between these base stations and the higher-level network.Further, the gateway apparatus 50 performs signaling concerning thehandover of a mobile station between the base stations a10, b20, c30,and d40. A mobile station (UE) 60 of the mobile communication system isconnected to the base station a10, and moves to be close to the basestation b20. When the mobile station 60 satisfies the condition toswitch the connection from the base station a10 to the base station b20,the mobile station 60 transmits PSC=2, which is an identification codeof the base station b20, to the base station a10. Between the basestations (the base station b20 and the base station d40) with the samePSC, the base station a10 or the gateway apparatus 50 selects the basestation with high success of the connection switching from the basestation a10. The base station a10 or the gateway apparatus 50 switchesthe connection of the mobile station 60 to the selected base station.

Next, details of the exemplary embodiment of the present invention areexplained with reference to the drawings. FIG. 2 is a view showing aconfiguration of the mobile communication system according to thisexemplary embodiment. FIG. 2 shows the state in which an UE 120 movesfrom a HNB#a100 cell to a HNB#b101 cell. As neighbor cells of theHNB#a100, there are the HNB#b101 cell, a HNB#c102 cell, and a HNB#d103cell.

PSC#1 is set to the HNB#a100 cell. Similary, PSC#2 is set to theHNB#b101 cell. PSC#3 is set to the HNB#c102 cell. PSC#2 is set to theHNB#d103. The HNB#a100 recognizes the HNB#b101, the HNB#c102, and theHNB#d103 as neighbor HNBs. That is, the HNB#a100 includes information(PSC, RNC-ID, and frequency information) on the HNB#b101, the HNB#c102,and the HNB#d103. Moreover, HNB-GW110 is configured to be mutuallycommunicative with the HNB#a100, the HNB#b101, the HNB#c102, and theHNB#d103.

FIG. 3 shows a list of the neighbor cells held by the HNB#a100. In otherwords, it is the list of information (PSC, RNC-ID, and UARFCN (frequencyinformation)) on the neighbor HNBs held by the HNB#a100. For example,the HNB#a100 recognizes “2” as the PSC, “BB” as the RNC-ID, and “X” asthe frequency for the HNB#b101.

Next, FIG. 4 shows an overview of an HNB Registration Procedure of HNBAP(Home Node B Application Part Signaling). Each HNB notifies theinformation on the HNB to the HNB-GW110 by the procedure shown in FIG. 4at the time when the operation is started (S201). Specifically, the HNBnotifies the information on the HNB by HNB REGISTER REQUEST message atthe time when the operation is started. Note that for details of the HNBRegistration Procedure of the HNBAP (Home Node B Application PartSignaling), see Section 8.2 in 3GPP Release 8 TS25.469.

The HNB-GW110 which received the HNB REGISTER REQUEST message stores theinformation on the HNB to a table in a database included inside. FIG. 5is a view showing the table in the database inside the HNB-GW110. TheHNB-GW110 holds the information on the PSC and UARFCN which are used byeach HNB that can communicate with the HNB-GW110.

After that, the HNB-GW110 transmits an HNB REGISTER ACCEPT message tothe HNB (S202). The above procedure enables the HNB-GW110 to providenecessary services to the HNB. Further, the abovementioned procedureenables the HNB-GW110 to exchange the information with the HNB and aCore Network.

Note that although the HNB Registration Procedure is defined in the 3GPPRelease 8, the corresponding part is not due to be changed in the 3GPPRelease 9.

FIG. 6 is a view showing the HNB REGISTER REQUEST message transmitted bythe HNB according to this exemplary embodiment. In the HNB REGISTERREQUEST massage transmitted by the HNB according to this exemplaryembodiment, parameters “Primary Scrambling Code” and “UARFCN” are newlydefined in addition to existing parameters of the HNB REGISTER REQUESTmessage. The “Primary Scrambling Code” is a parameter indicating a valueof the PSC assigned to the HNB that transmits the HNB REGISTER REQUESTmessage. The “UARFCN” (UMTS (Universal Mobile Telecommunications System)Absolute Radio Frequency Channel Number) is a parameter indicating thefrequency used by the HNB that transmits the HNB REGISTER REQUESTmessage. Note that for details of the HNB REGISTER REQUEST message, seesection 9.1.3 of the 3GPP Release 8 TS25.469.

FIG. 7 describes details of an RUA:DIRECT TRANSFER message transmittedfrom the HNB according to this exemplary embodiment to the HNB-GW110. Inthe RUA:DIRECT TRANSFER transmitted by the HNB according to thisexemplary embodiments, a parameter called “Confusion flag” is newlydefined in addition to existing parameters of the RUA:DIRECT TRANSFER.The “Confusion flag” is a parameter used when the PSC Confusion isgenerated in order for the HNB to notify to that effect. When the PSCConfusion is generated, the HNB sets the “Confusion flag” to “TRUE”, andtransmits the RUA:DIRECT TRANSFER message to the HNB-GW110. Note thatfor details of the RUA:DIRECT TRANSFER message, see Section 9.1.4 of the3GPP Release 8 TS25.468.

Note that in this exemplary embodiment, although the RUA:DIRECT TRANSFERmessage defines whether or not the PSC Confusion is generated, it is notlimited to this. For example, the generation of the PSC Confusion may benotified by describing the content in the RANAP message encapsulatedinside the RUA:DIRECT TRANSFER message.

Next, an operation of each components (HNB, HNB-GW, UE, and the like) ofthe mobile communication system according to this exemplary embodimentis explained. First, the procedure of the HNB Registration is explainedwith reference to FIGS. 4 and 5.

The HNB notifies the information on the HNB to the HNB-GW110 by the HNBREGISTER REQUEST message at the time when the operation is started(S201). At this time, the HNB REGISTER REQUEST message includes the“Primary Scrambling Code” and the “UARFCN”.

The HNB-GW110 which received the HNB REGISTER REQUEST message stores the“Primary Scrambling Code” and the “UARFCN” received from each HNB to thedatabase inside. The table in the database shown in FIG. 5 stores theinformation on the “Primary Scrambling Code” and the “UARFCN” of thefour HNBs (HNB#a, HNB#b, HNB#c, and HNB#d) in the HNB-GW110. Note thatin FIG. 5, all the four HNBs use the same frequency (“X”).

After the HNB-GW110 stores the information on the “Primary ScramblingCode” and the “UARFCN” to the table in the database, the HNB-GW110transmits an HNBAP:HNB REGISTRATION ACCEPT message to the HNB thattransmitted HNB REGISTER REQUEST message (S202). The process of the HNBRegistration is completed by transmitting the HNBAP:HNB RegistrationAccept message. Note that there is no charge in the HNBAP:HNBREGISTRATION ACCEPT message. Note that there is no change in theHNBAP:HNB REGISTRATION ACCEPT message from the existing message.

Next, the operation of the mobile communication system when there is aneed to execute the handover that is generated by move of the UE 120 isexplained. FIG. 8 is a sequence diagram showing the operation of themobile communication system at the time of executing the handover. Thatis, FIG. 8 shows the process when the UE 120 transmits anRRC:MEASUREMENT REPORT message in order for the UE 120 to handover tothe HNB#b101 by the UE 120 moving to be close to the HNB#b101 whilecommunicating with the HNB#a100. Further, in FIG. 8, the HNB-GW110 shallhold the table in the database shown in FIG. 5.

The UE 120 is in the state of communication with CS (Circuit Switch) orPS (Packet Switch) (S101). The UE 120 transmits the RRC:MEASUREMENTREPORT message including the information on the PSC of the HNB#b101(PSC=2) to the HNB#a100, which is the Source HNB, in order to hand overto the HNB#b101 (S302). When measurement of the frequency is instructed,the UE 120 includes in the RRC:MEASUREMENT REPORT message whether or notthe frequency being measured and the base station (HNB#a100) where theUE 120 exists is the same, and notifies the RRC:MEASUREMENT REPORTmessage.

The Source HNB (HNB#a100) which received the RRC:MEASUREMENT REPORTmessage is a cell including PSC=2, and selects the cell that satisfiesthe condition of frequency from the information on the neighbor cells ofthe Source HNB (FIG. 4). That is, when the frequency of the base stationnotified by the UE 120 in the RRC:MEASUREMENT REPORT message is the sameas the frequency of the Source HNB, the Source HNB selects the basestation including the frequency. On the other hand, when the frequencyof the base station notified by the UE 120 in the RRC:MEASUREMENT REPORTmessage is different from the frequency of the Source HNB, the SourceHNB selects the base station with the frequency different from thefrequency used by the Source HNB. However, both the HNB#b101 cell andthe HNB#d103 cell have PSC=2 here. Moreover, all of HNB#a, HNB#b, andHNB#d are using the same frequency (“X”). That is, the PSC Confusion isgenerated. Therefore, the Source HNB (HNB#a100) selects any one cell(the cell corresponding to the RNC-ID) at random. Here, RNC-ID=DD shallbe selected. Specifically, the Source HNB (HNB#a100) selects theHNB#d103 as the handover destination of the UE 120 (S303).

The Source HNB (HNB#a100) transmits the RUA:DIRECT TRANSFER messageincluding RNC-ID=DD selected in S303 to the HNB-GW110 (S304). Since thePSC Confusion is generated here, the Source HNB (HNB#a100) sets theConfusion flag in the RUA:DIRECT TRANSFER message to “TRUE”, andtransmits the RUA:DIRECT TRANSFER message.

As the Confusion flag in the RUA:DIRECT TRANSFER message is set to“TRUE”, the HNB-GW110 which received the RUA:DIRECT TRANSFER message canrecognize that the Source HNB (HNB#a100) selected the Target HNB atrandom. The database storing handover history, which is described later,does not exist inside the HNB-GW110 here. The database does not existbefore the handover is performed via the HNB-GW110. When the databasedoes not exist, the HNB#d103 as the Target HNB without handling the PSCConfusion (S305). The HNB-GW110 generates the RANAP:RELOCATION REQUESTmessage to be transmitted to the HNB#d103 including the transmittedRNC-ID.

The HNB-GW110 transmits the RANAP:RELOCATION REQUEST messageencapsulated in the RUA message to the HNB#d103, which is the identifiedTarget HNB (S306).

When the Target HNB receives the RANAP:RELOCATION REQUEST message, theTarget HNB registers the information on the UE 120 that performshandover and reserves the resource for the UE 120 (S307). Then, theTarget HNB transmits the RUA:DIRECT TRANSFER message encapsulating aRANAP:RELOCATION REQUEST ACKNOWLEDGE message to the HNB-GW110 (S308).

The HNB-GW110 which received the RUA:DIRECT TRANSFER message transmits aRANAP:RELOCATION COMMAND message to the Source HNB (HNB#a100) (S309).The Source HNB (HNB#a100) which received the RANAP:RELOCATION COMMANDmessage transmits Physical Channel Reconfiguration for instructingphysical channel reconfiguration to the UE 120 (S310).

The UE 120 which received the Physical Channel Reconfiguration attemptsto obtain wireless synchronization with the HNB#b101, which is thedesired handover destination. However, in S306, the HNB-GW110 transmitsthe RUA message (RUA:XXX) encapsulating the RANAP:RELOCATION REQUESTmessage to the HNB#d103. Therefore, the HNB#b101 does not register theinformation on the UE 120 that performs handover, and the like.Accordingly, the UE 120 fails the wireless synchronization with theHNB#b101. The UE 120 transmits an RRC:PHYSICAL CHANNEL RECONFIGURATIONFAILURE message to the Source HNB (HNB#a100) (S311).

The Source HNB (HNB#a100) which received the RRC:PHYSICAL CHANNELRECONFIGURATION FAILURE message transmits the RUA:XXX messageencapsulating a RANAP:RELOCATION CANCEL message to the HNB-GW110 (S312).

The HNB-GW110 recognized that the handover failed by not receiving aRANAP:RELOCATION DETECT message from the Target HNB, and further,receives the RANAP:RELOCATION CANCEL message from the Source HNB(HNB#a100). The HNB-GW110 creates a new database when there is no insidedatabase that stores the history of handover results. Then, theHNB-GW110 reflects the handover failure on the table (FIG. 9) in thedatabase (S313). Note that the HNB-GW110 may create the database in theinitialized state at the time of operation.

FIG. 9 is the table in the database that stores the history of handoverresults inside the HNB-GW110. As shown in FIG. 9, the table stores theinformation of whether or not the handover to the HNB, which is thetarget of the handover destination, from the HNB of each handover sourceis successful or not. In the abovementioned S313, as the handover fromthe HNB#a100 to the HNB#d103 has failed, the result of the failure isreflected on the table.

Note that although the table shown, in FIG. 9 is configured to store thenumber of handover successes and failures, it is not limited to this.For example, the table may be configured to store only the number ofhandover failures or successes.

After reflecting the success or failure of handover on the database, theHNB-GW110 transmits the RUA:XXX message encapsulating theRANAP:RELOCATION CANCEL ACKNOWLEDGE message to the Source HNB (S314). Bythe above process, the mobile communication system according to thisexemplary embodiment completes the handover process.

Next, in the state of the table shown in FIG. 9, the process of the casewhen the UE 120 further requests handover from the HNB#a100 to theHNB#b101 is explained. FIG. 10 is a sequence diagram showing a flow ofthe process.

The process of S101 and S302 to S304 is the same as the process shown inFIG. 9. The HNB-GW110 which received the RUA:DIRECT TRANSFER message canrecognize that the Source HNB (HNB#100 ) selected the Target HNB atrandom as the Confusion flag in the RUA:DIRECT TRANSFER message is setto “TRUE”.

Then, the HNB-GW110 refers to the table (FIG. 9) in the database showingthe handover history, and selects an appropriate HNB as the handoverdestination from the HNBs with the transmitted PSC. Specifically, theHNB-GW110 ranks the Target HNBs (the HNBs with the transmitted PSC) asdescribed below.

First, a row f the HNB, which is the handover source, is extracted fromthe table (FIG. 9) in the database showing the handover history. A rowof the HNB#a is extracted here. Next, the table holding the PSCinformation on each HNB shown in FIG. 5 is referred, the HNB with thesame PSC as the transmitted PSC is identified, and other HNBs areexcluded. Further, the HNB-GW110 refers to the table shown in FIG. 5 andexcludes the HNBs not using the same UARFCN as the TARGET RNC-ID fromthe candidates. This is for not generating the PSC Confusion even whenthe same PSC is used with different frequencies.

Then, the HNB with a low failure rate in the handover is highly rankedamong the remaining HNBs. Although HNB#b and HNB#d have the same PSC,HNB#b with the low failure rate is highly ranked. Such a series ofprocesses creates a list of ranked handover destination candidates asshown in FIG. 11. Then, the HNB-GW110 selects the highest ranked HNB#bas the handover destination (Target HNB) (S405).

Although in the above explanation, the list of handover destinationcandidates ranked as shown in FIG. 11 is generated according to thehandover history, it is not limited to this and the HNBs may be rankedby other methods. For example, the HNB-GW110 can notify the positioninformation thereof by an HNBAP:HNB LOCATION INFORMATION message fromeach HNB. When the PSC Confusion is generated, the HNB-GW110 uses thisposition information to preferentially select the HNB close to theSource HNB. Selection of the HNB using this position informationincreases the possibility of executing handover to the Target HNBintended by the UE 120.

The HNB-GW110 transmits the RUA:XXX message encapsulating theRANAP:RELOCATION REQUEST message to the HNB#b101 that is selected as theTarget HNB (S406). Subsequent process (From S107 to S114) is the same asthe process shown in FIG. 20.

By receiving the RUA:DIRECT TRANSFER message encapsulating aRANAP:RELOCATION COMPLETE message from the Target HNB, the HNB-GW110 canrecognize that the handover is normally complete. The HNB-GW110 reflectsthat the handover is successful on the table (FIG. 9) that stores thehandover history (S415). The subsequent process (S115 to S117) is thesame as the process shown in FIG. 3.

Next, the process leading to determination of the Target HNB by theSource HNB according to this exemplary embodiment is explained using theflowchart of FIG. 12. Firstly, the HNB receives a handover request fromthe UE 120 (S501). The Source HNB searches for a cell with the PSCincluded in the received handover request from a neighbor list (FIG. 3).When a plurality of cells are detected here (S502; Yes), that is, whenthe PSC Confusion is generated, the Confusion flag of the RUA:DIRECTTRANSFER message is set to “True” (S503). Then, the Source HNBdetermines the RNC-ID of the handover destination at random from theHNBs with the received PSC (S504).

On the other hand, when there is no plurality of cells with the PSCincluded in the received handover request in the neighbor list (FIG. 3)(S502: No), the Source HNB does not set the Confusion flag of theRUA:DIRECT TRANSFER message (S505). Accordingly, the Confusion flag is“False”. After that, the Source HNB selects the RNC-ID according to thehandover request from the UE 120 (S506).

The Source HNB transmits the RUA (RANAP User Adaption):DIRECT TRANSFERmessage including the selected RNC-ID to the HNB-GW110 (S507). The RANAP(Radio Access Network Application Part):RELOCATION REQUIRED message isencapsulated in the RUA:DIRECT TRANSFER message.

Nest, the process leading to the determination of the Target HNB by theHNB-GW110 according to this exemplary embodiment is explained using theflowchart of FIG. 13. The HNB-GW110 receives the RUA:DIRECT TRANSFERmessage encapsulating the RANAP:RELOCATION REQUIRED message from theSource HNB (S601). When the Confusion flag of the RANAP:RELOCATIONREQUIRED message is set to “FALSE” (S602: No), the HNB-GW110 transmitsthe RUA:XXX message encapsulating the RANAP:RELOCATION REQUEST messageto the Target HNB according to the transmitted NC-ID (S609).

When the Confusion flag of the RANAP:RELOCATION REQUIRED message is setto “TRUE” (S602: Yes), that is, when the PSC Confusion is generated, theHNB-GW110 refers to the table (FIG. 9) in the database showing thehandover history. The HNB-GW110 refers to the table and evaluateswhether or not there is success history of the handover among theplurality of HNBs with the received PSC (S603). When there is thesuccess history (S603: Yes), the HNB-GW110 ranks the HNBs in thedescending order of number of successes (S604). When there is no successhistory (S603: Yes), it is evaluated whether or not there is any failurehistory of the handover among the plurality of HNBs with the receivedPSC (S605). When there is a failure history (S605: Yes), the HNB-GW110ranks the HNBs in the ascending order of number of failures (S606).

When the HNB-GW110 ranks the plurality of HNBs with the same PSC as thereceived PSC, the RNC-ID of the highest ranked cell is selected as thehandover destination (S607). On the other hand, even when the Confusionfag is set to “TRUE” (S602: Yes), in the case when there is no successhistory and failure history in the table in the database showing thehandover history (S603: No and S605: No), the handover destination isselected at random (S608). At this time, as mentioned above, thefrequency information is referred and the handover destination selectedat random can be limited. After that, the HNB-GW110 transmits theRUA:XXX message encapsulating the RANAP:RELOCATION REQUEST message tothe Target HNB according to the selected RNC-ID (S609).

Note that in the abovementioned explanation, although the HNB-GW110 isexplained as a processing apparatus that selects a connectiondestination of the mobile station according to the connection historyinformation, it is limited to this and other apparatuses connected tothe HNB-GW110 may function as the processing apparatus, for example.

Next, an effect of the mobile communication system according to thisexemplary embodiment is explained. The HNB according to this exemplaryembodiment transmits to the HNB-GW110 the PSC and the frequency (UARFCN)assigned to the HNB. Accordingly, the HNB-GW 110 can recognize the PSCand the frequency of each HNB.

Moreover, as described above, the Confusion flag, which is the newparameter, is added to the RUA;DIRECTED TRANSFER message transmittedfrom the Source HNB to the HNB-GW110. When the PSC Confusion isgenerated, specifying this parameter enables the Source HNB to notify tothat effect to the HNB-GW110.

The HNB-GW110 includes inside a table in a database that storesexecution history of the handover (whether or not the handoversucceeded). Referring to the table enables an HNB-GW110 to select theHNB with high success rate of handover as the Target HNB even when thePSC Confusion is generated.

Second Exemplary Embodiment

The second exemplary embodiment of the present invention ischaracterized in that the Source HNB specifies a plurality of RNC-IDs.Hereinafter differences from the first exemplary embodiment are focusedand explained.

FIGS. 14A and 14B describe the Target ID included in theRANAP:RELOCATION REQUIRED message transmitted from the Source HNB to theHNB-GW110. It is configured in a way that the plurality of RCN-IDs canbe specified as compared to the configuration of the Target ID of therelated art. That is, the Source HNB defines a Target RNC-ID LIST as anew information element (IE) to the Target ID, can specify the pluralityof RNC-IDs to the Target RNC-ID LIST, and transmit them to theHNB-GW110. In the definition shown in FIG. 14, up to 16 RNC-IDs can bespecified. Note that for details of the RANAP:RELOCATION REQUIRED andthe Target ID, see the 3GPP Release 8 TS 25.413.

In this exemplary embodiment, in S304 of the process flow of thehandover shown in FIG. 10, when the PSC Confusion is generated, theSource HNB does not specify the Confusion flag and specifies all theRNC-IDs for the cells with the same PSC. The Source HNB transmits theRANAP:RELOCATION REQUIRED message including tire Target ID whichspecified the plurality of RNC-IDs to the HNB-GW110.

When the plurality of RNC-IDs are specified, the HNB-GW110 whichreceived the RANAP:RELOCATION REQUIRED message evaluates that the PSCconfusion is generated. Other processes are the same as that of thefirst exemplary embodiment.

Next, an effort of the mobile communication system according to thisexemplary embodiment is explained. As described above, the Source HNBcan transmit the RANAP:RELOCATION REQUIRED message including the TargetID which specified the plurality of RCN-IDs to the HNB-GW110. Then, theHNB-GW110 can select the handover destination from the cells concerningthe received RCN-ID without searching in the table (FIG. 5) managed bythe HNB-GW110.

Further, the above configuration enables the Source HNB to notify thatthe PSC Confusion is generated without specifying the Confusion flag.

Third Exemplary Embodiment

A third exemplary embodiment of the present invention is characterizedin that each HNB holds execution history of handover instead of theHNB-GW110. Differences from the first exemplary embodiment and thesecond exemplary embodiment are focused and explained.

FIG. 15 is view showing a configuration of the HNB according to thisexemplary embodiment. As illustrated, each HNB includes a database 130inside, and a table is held inside the database 130. In addition to thePSC, RNC-ID, and UARFCN, each HNB stores the number of handoversuccesses and the number of handover failures as a neighbor list. Thenumber of handover successes indicates the number of handover successesfrom the HNB that holds the table. Further, the number of handoverfailures indicates the number of handover failures from the HNB thatholds the table. Note that in this exemplary embodiment, the HNB-GW110does not hold the database (FIG. 9) concerning the handover history.

Each HNB holds only the information on the base station which composesits own cell and the neighbor cell to its own database. Therefore, thesize of the table that stores the handover history is smaller than thefirst exemplary embodiment and the second exemplary embodiment.

The process of the mobile communication system according to thisexemplary embodiment in the case when the UE 120 communicating using theHNB#a100 issues a handover request to the HNB#b100 is explained usingFIG. 16. Note that FIG. 16 shows an example of the handover failurecaused by the PSC Confusion in a similar manner as FIG. 8.

The process of S101 and S302 is the same as the process shown in FIG. 8.The Source HNB (HNB#a100) refers to the PSC included in the receivedRRC:MEASUREMENT REPORT message and evaluates the RNC-ID of the handoverdestination (S703). The value of the received PSC is “2” here and thereare a plurality of rows with PSC=“2” in the table in the database insidethe HNB#a100. All the neighbor base stations are using the samefrequency (“X”). Therefore, the Source HNB evaluates that the PSCConfusion is generated.

When it is evaluated that the PSC Confusion is generated, the Source HNBrefers to the table in the database that stores the handover history.Then, the Source HNB compares the number of handover successes andfailures for the cells with the received PSC, and ranks them. When thetable inside the Source HNB (HNB#a100) shown in FIG. 15 is referredhere, both the number of handover successes and the number of handoverfailures for the HNB#b101 and the HNB#d103 are zero. Therefore, theSource HNB (HNB#a100) selects the handover destination at random fromthe HNB#b101 and the HNB#d103. In the following example, the Source HNB(HNB#a100) examines the case of selecting the HNB#d103.

The Source HNB transmits to the HNB-GW110 the RUA:DIRECT TRANSFERmessage encapsulating the RANAP:RELOCATION REQUIRED message includingthe RNC-ID (“DD”) of the selected HNB#d103 (S704). The subsequentprocess of S305 to S309 is the same as the process shown in FIG. 8.

The Source HNB which received the RANAP:RELOCATION COMMAND message fromthe HNB-GW110 transmits RRC:Physical Channel Reconfiguration to the UE120 (S710). When the Source HNB receives the RRC:PHYSICAL CHANNELRECONFIGURATION FAILURE message from the UE 120 after transmitting theRRC:Physical Channel Reconfiguration (S711), the Source HNB evaluatesthat the handover failed.

When the handover failed, the Source HNB updates the failure on thetable in its own the database (S712). The table of the HNB#a100, whichis the updated Sources HNB, is shown in FIG. 17.

Next, the process of the mobile communication system according to thisexemplary embodiment for the case when the UE 120 which is communicatingusing the HNB#a100 issues a handover request to the HNB#B101 isexplained using FIG. 18.

The process of S101 and S302 is the same as the process shown in theFIG. 16. After that, the Source HNB (HNB#a100) refers to the PSCincluded in the received RRC:MEASUREMENT REPORT message and evaluatesthe RNC-ID of the HNB, which is the handover destination (S803). In asimilar manner as FIG. 16, the Source HNB (HNB#a100) evaluates that thePSC Confusion is generated.

When it is evaluated that the PSC Confusion is generated, the Source HNBrefers to the table in the database that stores the handover history andselects the handover destination. Both the number of handover successesand the number of handover failures for the HNB#B101 are zero. On theother hand, the number of handover failures for the HNB#d103 is one.Therefore, the Source HNB selects the HNB#b101 as the handoverdestination. The Source HNB transmits to the HNB-GW110 the RUA:DIRECTTRANSFER message encapsulating the RANAP:RELOCATION REQUIRED messageincluding RNC-ID (“BB”) of the selected HNB#b101 (S804). The subsequentprocess in S305 to S309 is the same as the process shown in FIG. 8. Theprocess in S110 to S117 is the same as the process shown in FIG. 20.

When a RANAP:IU RELEASE COMMAND message and a HNBAP:E DE-REGISTER arereceived from the HNB-GW110 after the RANAP RELOCATION COMMAND istransmitted, the Source HNB evaluates that the handover succeeded. Whenthe handover succeeded, the Source HNB updates the Success on the tablein its own database.

Next, FIG. 19 is shown for the process at the time when the Source HNBdetermines the Target HNB according to this exemplary embodiment. In asimilar manner as FIG. 13, the handover destination is determinedaccording to the handover history (S603 to S608).

Next, FIG. 19 is shown for the process at the time when the Source HNBdetermines the Target HNB according to this exemplary embodiment. In asimilar manner as FIG. 13, the handover destination is determinedaccording to the handover history (S603 to S608).

Next, an effort of the mobile communication system according to thisexemplary embodiment is explained. As described above, in this exemplaryembodiment, the Source HNB holds history of handover successes andfailure to the HNBs composing the neighbor cells of the Source HNB. TheSource HNB determines the handover destination of the UE 120 accordingto the history. As the Source HNB holds only the history regarding theHNBs that compose the neighbor cells, the amount of the information isless than the history information held by the HNB-GW110. Therefore,there is a lower possibility that the same PSC is assigned to the HNBsheld by the Source HNB. Even when the PSC Confusion is generated, thenumber of base stations to be handover candidates is reduces and thefailure rate of the handover will be even lower.

Note that the present invention is not limited to the above exemplaryembodiments, but can be modified as appropriate without departing fromthe scope. For example, although an example of using the Intra CGS andalso the Intra HNB-GW for the mobile communication system is describedin the first and second exemplary embodiment, it is not limited to thisand it can be applied to the environment using the Inter CSG and theIntra HNB-GW. In the case of the environment using the Inter CSG and theIntra HNB-GW, the CN will perform the process equivalent to a part ofthe abovementioned handover process. Even in the environment using theInter CGS and the Intra HNB-GW, a success or a failure of the handoveris evaluated according to whether the HNB-GW receives theRANAP:RELOCATION CANCEL message or the RANAP:RELOCATION COMPLETEmessage, and updates the database.

Further, although an example of using the Intra CGS and also the IntraHNB-GW for the mobile communication system is described in the thirdexemplary embodiment is explained, it is not limited to this and it canbe applied to the environment using the Inter CSG and the Intra HNB-GW.In the case of the environment using the Inter CSG and the Intra HNB-GW,a success or a failure of the handover is evaluated according to whetherthe Source HNB receives the RRC:PHYSICAL CHANNEL RECONFIGURATION FAILUREmessage of the RANAP:IU RELEASE COMMAND message, and updates thedatabase.

Note that the abovementioned process for determining the handoverdestination can be realized by causing a CPU (Central Processing Unit)to execute a computer program.

The program can be stored and provided to a computer using any type ofnon-transitory computer readable media. Non-transitory computer readablemedia include any type of tangible storage media. Examples ofnon-transitory computer readable media include magnetic storage media(such as floppy disks, magnetic tapes, hard disk drives, etc.), opticalmagnetic storage media (e.g. magneto-optical disks), CD-ROM (compactdisc read only memory), CD-R (compact disc recordable), CD-R/W (compactdisc rewritable), and semiconductor memories (such as mask ROM, PROM(programmable ROM), EPROM (erasable PROM), flash ROM, RAM (random accessmemory), etc.). The program may be provided to a computer using any typeof transitory computer readable media. Examples of transitory computerreadable media include electric signals, optical signals, andelectromagnetic waves. Transitory computer readable media can providethe program to a computer via a wired communication line (e.g. electricwires, and optical fibers) or a wireless communication line.

The whole or part of the exemplary embodiments disclosed above can bedescribed as, but not limited to, the following supplementary notes.

(Supplementary Note 1)

A processing apparatus that, when a connection of a mobile station isswitched from a first base station to a second base station, selects thesecond base station from a plurality of base stations according toconnection history information indicating a success or a failure of pastswitching of the connection from the first base station to at least oneof the plurality of base stations.

(Supplementary Note 2)

The processing apparatus according to Supplementary note 1, wherein theprocessing apparatus selects the second base station using theconnection history information from the base station assigned with aspreading code that is same as the spreading code of the base stationtransmitted by the mobile station for notifying the base station thatsatisfies a condition to switch the connection among the plurality ofbase stations.

(Supplementary Note 3)

The processing apparatus according to Supplementary note 1 or 2, whereinthe processing apparatus preferentially selects the base station with arelatively high success rate of the connection as the second basestation in the connection history information.

(Supplementary Note 4)

The processing apparatus according to one of Supplementary notes 1 to 3,wherein when the mobile station notifies information on the frequency ofthe base station that satisfies the condition to switch the connection,the processing apparatus selects the second base station from the basestation that use the same frequency as the frequency among the pluralityof base stations.

(Supplementary Note 5)

A mobile communication system comprising:

-   -   a first base station that generates a first cell and can be        connected to a mobile station;    -   a gateway apparatus that communicatively connects the first base        station and a plurality of base stations to a higher-level        network; and    -   a processing means that, when a connection of the mobile station        is switched from the first base station to a second station that        is included in the plurality of base stations, selects the        second base station from the plurality of base stations        according to connection history information indicating a success        or a failure of past switching of the connection from the first        base station to at least one of the plurality of base stations.

(Supplementary Note 6)

The mobile communication system according to Supplementary note 5,wherein the processing means selects the second base station using theconnection history information from the base station assigned with aspreading code that is same as the spreading code of the base stationtransmitted by the mobile station for notifying the base station thatsatisfies a condition to switch the connection.

(Supplementary Note 7)

The mobile communication system according to Supplementary note 5 or 6,wherein the processing means preferentially selects the base stationwith a relatively high success rate of the connection as the second basestation in the connection history information.

(Supplementary Note 8)

The mobile communication system according to one of Supplementary notes5 to 7, wherein when the mobile station notifies information on afrequency of the base station that satisfies the condition to switch theconnection, the processing means selects the base station to which themobile station is connected from the base stations that use the samefrequency as the frequency among the plurality of base stations.

(Supplementary Note 9)

The mobile communication system according to one of Supplementary notes5 to 8, wherein

-   -   the first base station notifies the processing unit of a flag        indicating whether or not the plurality of base stations exist        that are assigned with the same spreading code as the spreading        code of the base station transmitted by the mobile station to        notify the base station that satisfies the condition for        switching the connection, and    -   when receiving the flag, the processing means selects the second        base station according to the connection history information.

(Supplementary Note 10)

The mobile communication system according to one of Supplementary notes5 to 8, wherein

-   -   when the plurality of base stations exist that are assigned with        the same spreading code as the spreading code of the base        station transmitted by the mobile station for notifying the base        station that satisfies the condition to switch the connection,        the first base station notifies the processing means of all the        plurality of base station candidates, and    -   the processing means selects the second base station according        to the connection history information from the plurality of base        station candidates notified from the first base station.

(Supplementary Note 11)

The mobile communication system according to one of the Supplementarynotes 5 to 10, wherein the processing means is disposed in the gatewayapparatus.

(Supplementary Note 12)

The mobile communication system according to one of Supplementary notes5 to 8, wherein

-   -   the processing means is disposed in the first station, and    -   when the plurality of base stations exist with the same        spreading code as the spreading code of the base station        transmitted by the mobile station for notifying the base station        that satisfies the condition to switch the connection, the first        base station selects the second base station according to the        connection history information from the plurality of base        stations with the same spreading code.

The present application claims priority rights of and is based onJapanese Patent Application No. 2009-286823 filed on Dec. 17, 2009 inthe Japanese Patent Office, the entire contents of which are herebyincorporated by reference.

Reference Signs List

-   10 BASE STATION A-   20 BASE STATION B-   30 BASE STATION C-   40 BASE STATION D-   50 GATEWAY APPARATUS-   60 MOBILE STATION-   100 HNB#a-   101 HNB#b-   102 HNB#c-   103 HNB#d-   110 HNB-GW-   120 UE

What is claimed is:
 1. A method of operation by a Home Node B (HNB),comprising: including a Primary Scrambling Code (PSC) of a cell servedby the HNB in a first HNB Application Part (HNBAP) message that is a HNBREGISTER REQUEST message: transmitting the HNB REGISTER REQUEST messageincluding the PSC to a Home Node B Gateway (HNB-GW) configured toconnect another Home Node B (HNB) that is different from the HNBtransmitting the HNB REGISTER REQUEST message; and receiving a secondHNB Application Part (HNBAP) message that is a HNB REGISTER ACCEPTmessage in response to the HNB REGISTER REQUEST message.
 2. A home NodeB Gateway (HNB-GW) comprising: a unit configured to connect to a HomeNode B (HNB); a receiver configured to receive a first HNB ApplicationPart (HNBAP) message that is a HNB REGISTER REQUEST message including aPrimary Scrambling Code (PSC) of a cell served by the HNB; and atransmitter configured to transmit a second HNB Application Part (HNBAP)message that is a HNB REGISTER ACCEPT message in response to the HNBREGISTER REQUEST message including the PSC.
 3. A Home Node B (HNB)comprising: a unit configured to include a Primary Scrambling Code (PSC)of a cell served by the HNB in a first HNB Application Part (HNBAP)message that is a HNB REGISTER REQUEST message; a transmitter configuredto transmit the HNB REGISTER REQUEST message including the PSC to a HomeNode B Gateway (HNB-GW) configured to connect another Home Node B (HNB)that is different from the HNB transmitting the HNB REGISTER REQUESTmessage; and a receiver configured to receive a second HNB ApplicationPart (HNBAP) message that is a HNB REGISTER ACCEPT message in responseto the HNB REGISTER REQUEST message.
 4. A mobile station comprising: acommunication unit configuration to communicate with a first Home Node B(HNB) that includes a Primary Scrambling Code (PSC) of a cell served bythe first HNB in a first HNB Application Part (HNBAP) message that is aHNB REGISTER REQUEST message, transmits the HNB REGISTER REQUEST messageincluding, the PSC to a Home Node B Gateway (HNB-GW) configured toconnect a second Home Node B (HNB) that is different from the first HNBtransmitting the HNB REGISTER REQUEST message, and receives a second HNBApplication Part (HNBAP) message that is a HNB REGISTER ACCEPT messagein response to the HNB REGISTER REQUEST message, wherein thecommunication unit is configured to communicate the second HNB.